An asteroid discovered just a month ago is making a close approach to the Earth.

Although there is no danger of collision with it, astronomers say that its proximity reminds us just how many objects there are in space that could strike our planet with devastating consequences.

Moving closer to the Sun, the asteroid is passing by at less than three times the Moon's distance from us - just 830,000 kilometres (510,000 miles) away on 7 January, which is close in cosmic terms.

It is thought to be 300 metres in size - large enough to wipe out an entire country if it struck the Earth.

'Potentially hazardous'

2001 YB5 was discovered in early December by the Neat (Near Earth Asteroid Tracking) survey telescope observing from Mount Palomar in California, US.

Astronomers call it an Apollo object because it has a highly elliptical orbit that crosses the orbits of Mars, Earth, Venus and Mercury. It circles the Sun every 1,321 days.

Astronomers also add that it is "potentially hazardous", meaning there is a slim chance that it may strike the Earth sometime in the future.

As it approached the Earth, it was observed by the Klet Observatory in the Czech Republic by astronomers Jana Ticha and Milos Tichy, who tracked it on 5 January.

Such a "close encounter" is rare but not unprecedented. However, the only other known object that will come closer to the Earth is an asteroid called 1999 AN10, which will pass a shade closer on 7 August, 2027.

Widespread devastation

2001 YB5's brightness suggests it is a rocky body about 300 metres across.

If it struck the Earth a 300-metre object would not be a global killer: to wipe all life off the face of our planet an object would have to be about 1 km in size. But 300 metres is more than enough to cause widespread devastation.

There is nothing we could have done about it

Dr Benny Peiser

If it struck land, it would wipe out an entire country. If the impact point were London, then scientists estimate there would be total devastation for 150 km and severe destruction for a further 800 km, meaning that not only would the UK be destroyed but France and the Low Countries as well.

If it struck the ocean, the destruction would be more widespread. It would trigger tsunamis that would devastate most coastal cities.

Little warning

According to experts, the recent discovery and close approach of 2001 YB5 suggests that something nasty could creep up on us at any time.

Dr Benny Peiser of Liverpool John Moores University, UK, told BBC News Online: "The fact that this object was discovered less than a month ago leads to the question of if we would have had enough time to do anything about it had it been on a collision course with us.

"Of course the answer is no; there is nothing we could have done about it.

"It is a reminder of the objects that are out there. It is a reminder of what is going to happen unless we track them more efficiently than we do and make better preparations to defend our planet," says Dr Peiser.